The present invention relates to devices for load carrying structures, consisting of laminated wood.
The general objective is to improve load carrying structures by increasing the utilization of the volume of the materials and to introduce pre-stressed forces.
Due to the lack of homogeneous strength and the natural dimensions of wooden materials, it is common to manufacture wooden beams by gluing together relatively slender, finger-jointed lamells. These types of beams are referred to as laminated beams and are produced in varying dimensions. Laminated beams obtain a high grade of homogeneous quality in the materials and consequently a high degree of allowable and real load carrying capacity These beams are ordinarily produced with a rectangular cross-section. This is an advantageous shape in case of fires. With reference to the strength of beams, the load bearing capacity depends on the ability to resist compression in the upper and tension forces in the lower part, while the shear forces in the middle of the section are relatively small. A rectangular cross-section is therefore not an ideal shape, because the material in the middle of the section is utilized only to a very small degree.
It is known that different beams have been made to imitate the usual metal beam section with a reduced material volume in the middle of the cross-section.
It is also known from different projects to improve wooden beams, that steel members have been installed in both the upper and lower parts.
The above-mentioned examples to improve wooden beam does not indicate that the desired, favorable results, have been reached, because wooden beams with the rectangular cross-section still tend to dominate the market.